Thomas ruddiman johnston



(No Model.)

T. R. JOHNSTON. BACKING FOR STONES FOR LITHOGRAPHIO PURPOSES.

No. 433,349. Patented July 29, 1890.

FIG '5 nrnnr rFrcE.

THOMAS RUDDIMAN JOHNSTON, OF LONDON, ENGLAND.

BACKING FOR STONES FOR LITHOGRAPHIC PURPOSES.

SPECIFICATION forming part of Letters Patent No. 433,349, dated July 29, 1890.

Application filed April 10 1839 Serial No. 306,644. (No model.)

To all whom it may concern:

Be it known that I, THOMAS RUDDIMAN JOHNSTON, map publisher, a subject of the Queen of Great Britain, residing at 26 Charterhonse Square, in the county of Middlesex, England, have invented certain new and use ful ImprovementsConnected with Stones for Lithographic Purposes; and I do hereby declare that the following is a full, clear, and exact description of the invention, which will enable others skilled in the art to which it appertains to make and use the same.

Of late years the general use of great numbers of the larger sizes of steam-printin machines and other causes have led to a great scarcity in the better quality of suitable lithographic stones, and as. the price'of these is considerably higher in proportion than that of smaller sizes it has been suggested that the stones might be cut into comparatively thin slabs and backed in some way with a cheaper material. It has also been proposed to strengthen lithographic stones with a backing of artificial stone composed of ground granite, sand, or like material, and Portland, Roman, or other like cement; but in practice this backing, by reason of its hard and unyielding character, caused the lithographic slabs to become unlevel, and they have broken when printed from, or without having been printed from they have been found to be cracked from some peculiar action of the cement used. In other cases the stones and backing came apart in use. It has also been proposed to cement backin to the stones by means of sulphur; but this, like plaster-ofparis, becomes entirely too refractory or brittle, and being of this unyielding nature it frequent] y cracks under the pressure necessarily brought to bear 011 the stone.

Now according to my invention I avoid the use of cements of the character hereinbefore referred to forbinding the ground stone, sand, 850., together, and I employ in lieu thereof asphalt, bitumen, pitch, or other like slightlyelastic adhesive matters or cements, or combinations of the same,which will readily melt by heat at a comparatively low temperature without the addition of water. I mix these materials with chips of stone, ground stone, sand, gravel, or other suitable solid material heretofore employed as a backing to the lithographic stone, or as a cement for securing the lithographic stone to a natural or artifi-. .cial stone backing.

The great advantage in substituting asphalt, bitumen, pitch, or other like matters or cements for the materials heretofore employed is that the backing, when made of the former and cemented to the slab by a like substance or cement, forms a slightly elastic 0r yielding base or backing for the slab, and

will take up the inequalities of the strain that may be caused by inequalities in the cement or in the backing proper, and thus avoid the,

as follows: I take aslab of lithographic stone and heat it in any convenient manner to about the melting-point of the cement used say, as an example, Seyssel asphalt. The asphalt having been melted with a small quantity of pitch or mineral tar and allowed to boil for four or five hours to remove the volatile oils, I then paint the back of the slab of stone (0 with this melted asphalt. To the edges of the face of the stone a, I then paste bands I), of paper, and having laid the slab face downward I fold these upward, joining them together, so that they, with the back of the stone (1, will form a shallow trough, and I support the paper I) at each side with a strip of wood 0, which strips may be long enough to suit various sizes of stones, in which case they are arranged as represented at Fig. 1, and they are preferably fixed together by staple-formed connecting-irons d; or I form a trough on the back of the stone in any other convenient manner. I then pour a small quantity of the melted asphalt into the trough, dropping at once into it the chips of stone, ground stone, sand, gravel, or other material, which has been previously heated. More asphalt is run in and more stone or other like material added until the desired thickness is attained. The surface of the compound forming the backing is then pressed and flattened, after which it is left tocool, by

which means a solid durable backing is firmly attached to the slab of lithographic stone a,

which backing is not liable to twist or warp in setting, nor to become accidentally detached from the slab of lithographic stone at. a The stone or other like material may, if desired, be previously mixed with the asphalt.

To join a slab of lithographic stone at to a slab of other natural or artificial stone (5*, I

heat both of these until they are warmer than 1 material used to connect the slab of lithographic stone a and the backing stone e* together. The slab of lithographic stone at and the backing e*, I now clamp firmly together by means of screw-clamps g, or by other suitable means, and having pasted paper 1) around or otherwise closed three sides of the space between the two stones to prevent the escape of the asphalt or other like cementing material, I turn the stones up on edge and pour the melted asphalt or other like cementing material between them.

Having fully described my invention, what I desire to claim and secure by Letters Patent is 1. A-lithographic stone having a backing composed of slightly-elastic material 06-,

mented thereto by means of a slightly elastic cement, substantially as set forth.

2. A backing for lithographic stone, consisting of eithernatural orartificial stone connected to they slab of lithographic stone by asphalt, bitumen pitch, or other adhesive slightly-elastic material capable of melting at comparatively low temperatures, substantially as herein described.

3. A backing for lithographic stone, consisting of asphalt, bitumen, pitch, or other adhesive slightly-elastic material capable of melting at comparatively low temperatures, or compounds of the same, mixed with chips of stone, ground stone, sand, gravel, or other material and connected to the lithographic stone by such like cements or-materials, substantially as herein described.

4. A cement for combining materials to form a backing to slabs of lithographic stone, and to connect the same or other backing thereto, composed of slightly-elastic adhesive material capable of being readily melted by heat at a comparatively low temperature without the addition of water, substantially as herein described, and for the purpose stated.

5. Astone for lithographic purposes, consisting of a slab of lithographic stone, and a backing cemented thereto by a slightly-elastic adhesive material capable of being readily melted by heat at a comparatively low temperature Without the addition of Water, substantially as herein described, and for the purpose stated.

6. A lithographic stone provided with a backing consisting of asphalt, bitumen, or pitch and some comminuted solid substance incorporated therewith cemented to said stone by means of a slightly-elastic cement,

such as asphalt, bitumen, or pitch, substantially as set forth.

THOMAS RUDDIMAN JOHNSTON. WVitnesses:

B. J. B. MILLS, CLAUDE K. MILLS, Both of 23 Southampton Building, London. 

